A large portion of the estimated $2.2 trillion stroke-related costs estimated in the U.S. between 2005 and 2050 pertains to the cost of care during the recovery period after the brain trauma, which in turn is highly correlated with the level of disability. These figures point to the urgency of improving post stroke neurorehabilitation, particularly since there are no drugs available, nor are there any in the pipeline, to facilitate functional recovery after stroke. Until recently, only few studies focused on the basic mechanisms and potential improvement of post stroke functional recovery. Previous findings from our laboratory, and some promising human data about non-invasive brain stimulation in recovering stroke patients, point to an imbalance between excitatory/inhibitory cortical circuits as a major obstacle in post stroke functional recovery. We will use a mouse model of stroke to examine how the outcome of brain stimulation after the injury can be improved. Photothrombotic stroke will be induced in the motor cortices of mice using a novel stroke model developed for focal ischemia induction in awake freely moving animals. We will test the hypothesis that the modulation of a highly specific component of the affected cortical microcircuits will provide the best outcome on functional recovery after stroke. Four different transgenic mouse lines will be used for specific optogenetic manipulations of excitatory and inhibitory cortical microcircuits in the peri-infarct region, or in the equivalent cortical area on the contralateral hemisphere. 1) Cortical pyramidal cells will be stimulated in the peri-infarct zone to test the effects of ipsilesonal stimulation of excitatory circuits; 2) The activity of inhibitory GABAergic cells will be suppresse in the peri-infarct zone to reduce the enhanced inhibition observed after stroke, previously shown by our lab to obstruct the path to functional recovery; 3) Peri-infarct glial cells will be stimulated to test whether impaired glial activity and a secondarily reduced GABA uptake may contribute to the observed enhancement in inhibition and the ensuing delayed functional recovery; 4) Contralateral to the infarct, GABAergic cells will be stimulated to dampen the output of the healthy motor cortex which may act to lower the activity of the lesioned side. Optical stimulation will be carried out for 5 days after stroke induction in daily 1-hour sessions, based o protocols of non-invasive, but non-specific brain simulation in human subjects. In addition to more traditional measures of functional motor recovery in mice, we will use a novel automated measurement of the mouse's movements on an air-supported sphere, which can be subjected to better quantification than previously used measures of motor recovery. By introducing novel approaches in stroke induction, stimulation therapy, and outcome metrics, the project addresses scientific questions related to the enormous economical and health burdens of stroke in both the U.S. and worldwide. The project will also identify specific target systems for promoting rehabilitation in the clinical practice, to result in a healthier life and an earlier functional reovery of stroke victims.